ACTA ACUSTICA UNITED WITH ACUSTICA Vol. 99 (2013) 30 – 39 DOI 10.3813/AAA.918585 Measurements and Analysis of the Epidaurus Ancient Theatre Acoustics Sotirios Psarras 1) , Panagiotis Hatziantoniou 2) , Mercury Kountouras 3) , Nicolas-Alexander Tatlas 2) , John N. Mourjopoulos 2) , Dimitrios Skarlatos 2) 1) ACOU Acoustics Engineering, Athens, Greece. acou@otenet.gr 2) University of Patras, Patras, Greece. hagianto@wcl.ee.upatras.gr, ntatlas@upatras.gr, mourjop@upatras.gr, skarlat@mech.upatras.gr 3) HEAR Hellenic Acoustics Research, Thessaloniki, Greece. mk@hear.gr Dedicated to the memory of Stamatis Vassilantonopoulos (1947–2010) Summary Extensive results are presented for acoustic and meteorological measurements at the ancient open theatre of Ep- idaurus. The analysis of the results, illustrates most aspects of the theatre’s acoustic properties, indicating the pattern and mechanism for the early reflections, the spectral response of the theatre, aspects of time-frequency response interaction and aspects of the spatial impression. The results also verify predictions of earlier acoustic models for this theatre and indicate no significant effects from environmental factors such as temperature, humid- ity and wind variations across the theatre. Measurements with the theatre partially full with audience show no change with respect to speech intelligibility. The results restate the renowned exceptional acoustic characteristics of the theatre for speech, for all listener positions. PACS no. 43.55.-n, 43.58.-e 1. Introduction The evolution of the classical-era theatre architecture from the 6th century BC to the beginning of the Hellenistic period in the 4th century, an age that saw the flourish- ing of mathematics and acoustics via the influence of Pythagorean science, led to amphitheatres with improved acoustics and visibility and culminates with the theatre of Epidaurus. The theatre is located at the eastern Pelopon- nese and was constructed in the sanctuary of Asclepius, the god of health and medicine, noting also that the ancient Greeks’ interest in the voice, speech, music and acoustics is based upon their theory of sound as a cathartic force. The name “Epidauros” is etymologically related to “δρα επi της α ´ υρας ”, indicating a place either affecting the hu- man aura, or been affected by the wind. Today it represents the best preserved of the classical Greek theatres and its remarkable acoustics with renowned speech intelligibility for audiences up to 14500 people, raise the interest both of experts and visitors. The theatre is functional, hosting mainly theatrical acts during the summer months. For a long time, acousticians have discussed and exam- ined the theatre’s properties [1, 2], but in the past, mainly due to equipment limitations, the acoustic measurements of the theatre [3] did not fully explain the reasons for such Received 29 April 2012, accepted 10 October 2012. acoustic performance. A detailed computer acoustic sim- ulation of the theatre was performed by Vassilantonopou- los and Mourjopoulos in 2002 [4], which predicted high speech intelligibility and described the paths for the the- atre’s early reflections. These results were confirmed in 2004 by detailed measurements for the same source- receiver positions [5, 6]. The measurements also revealed a frequency response dominated by a dip at approximately 180 Hz and an amplification of the 500–1500 Hz region. Note that the good correlation between ancient theatre computer modelling and measurements was also discussed in [7]. To analyse the theatre’s acoustics, Declercq and Dekey- ser [8] employed a geometric-based acoustic modelling method incorporating multiple orders of diffraction and concluded that the backscattered sound from the cavea amplifies high frequencies (above 500 Hz) more than low frequencies, thus proposing this as reason for the high speech intelligibility. Given the importance of the reflec- tion patterns in open-air theatres –but not specifically for Epidaurus– Farnetani et al. [9] studied such effects with measurements both in-situ and in scale models, also indi- cating the importance of the direct sound, the two early re- flections from the floor and stage building (when present) and reflections that correspond exactly to seven step edges behind the microphone position. Following this, the effect of the ground floor and cavea tier steps specular reflections and edge diffraction was also studied in [10]. Lokki et al. [11] developed a model of the lower cavea of the Epidau- 30 © S. Hirzel Verlag · EAA